Reciprocating piston and crank internal combustion engines having a four phase thermodynamic cycle have enjoyed wide use for the last three-quarters of a century not only as prime movers of vehicles but also in a wide variety of industrial applications. This wide acceptance is due to their reliability, low cost compared to alternative prime movers, and better torque vs. RPM characteristics.
The reciprocating piston and crank engine develops its maximum torque near the upper end of the engine's range. With the use of a suitable transmission, this high torque at high speed characteristic can be converted advantageously to high torque at a variety of speeds. These engines generally have a fixed piston displacement for each revolution of the crank and under high speed and low load conditions, this results in an excessive consumption of fuel.
Attempts have been made to reduce this problem by reducing the number of operable cylinders in response to increases in output speed. For example, it has been proposed in an eight cylinder engine after the engine reaches a certain speed that the valves associated with two or four of the cylinders be locked closed preventing intake or exhaust from these cylinders. While this may achieve a desired displacement reduction, it does not effect any significant reduction in fuel consumption because of the energy required to reciprocate and rotate the "closed down" pistons, rods and crank arms.
Variable displacement motors of the rotary annularly arrayed piston type have found considerable success as pumps or motors in the art of hydrostatic drives, but have not attained any significant success as internal combustion engines. These devices generally include a cylinder block, having annularly arrayed cylinders therein, that slideably engages a fixed valve plate having inlet and outlet ports. Pistons slideable in the cylinder block engage a tilted cam sometimes referred to as a "swashplate" that provides the reciprocating movement of the pistons as the cylinder block rotates. The displacement of the motor is varied by changing the angle of the swashplate and can easily be reduced to zero when perpendicular to the axis of the cylinder block, a feature which is desirable in many applications.
One of the disadvantages in using this rotary reciprocating piston motor as a variable displacement internal combustion engine is that as the displacement is varied, the compression ratio varies dramatically. The compression ratio is defined as CR=Stroke Length+Clearance Volume/Clearance Volume, where clearance volume is the volume of the cylinder with the piston in top dead center. Internal combustion engine fuels have, for a given fuel, a limited range of combustability, referred to as octane rating. The use of these fuels in the rotary reciprocating piston engine results in either under compression or over compression of the fuel, and this results in incomplete combustion and unwanted compression ignition. This inefficient burning of the fuel outweighs any benefits from the displacement varying capability of the rotary cylinder block motor.
Another, and related, problem in engines of the reciprocating piston and crank type (not the rotary cylinder block engine) is that their compression ratios are generally fixed or difficult to vary. This, of course, is because the crank throw or cylinder head position cannot be readily changed. In today's atmosphere of new petroleum fuels and petroleumalcohol fuels, it is desirable that an internal combustion engine be capable of using a variety of fuels efficiently. To do this, however, it is necessary to have an engine with a variable compression ratio, and thus far no practical engine of the reciprocating piston and crank type has been developed that achieves that end.
It is a primary object of the present invention to ameliorate the above problems, in internal combustion engines of the reciprocating piston and crank type.